Method of sharpening twist drills

ABSTRACT

METHOD OF SHARPENING TWIST-DRILLS HAVING A POINT COMPRISING AT LEAST TWO SYMMETRIC LIPS EACH FORMED WITH A CUTTING EDGE, CHARACTERIZED IN THAT THE TWIST-DRILL POINT IS GROUND TO IMPART A PRRAMIDAL CONFIGURATION THERETO   WITH THE VERTEX OF THE PYRAMID CENTERED AUTOMATICALLY TO THE TWIST-DRILL AXIS.

- Dec. 14, 1971 c ROCHET I 3,626,645

METHOD OF SHARPENING TWIST DRILLS Filed Oct. 10, 1969 United States Patent O Int. (:1. B24b 1/00 U.S. Cl. 51--288 4 Claims ABSTRACT OF THE DISCLOSURE Method of sharpening twist-drills having a point comprising at least two symmetric lips each formed with a cutting edge, characterized in that the twist-drill point is ground to impart a pyramidal configuration thereto with the vertex of the pyramid centered automatically to the twist-drill axis.

The present invention relates to an improved method of sharpening twist drills notably of the type used for drilling metals and alloys, and is directed to increase the wear resistance of the twist drill tip as well as the drilling precision of these tools.

Sharpening a twist drill according to conventional methods comprises as a rule two separate steps:

(1) Forming the lip relief angle of the point cutting edges of the twist drill by means of tapered or fiat surfaces;

(2) Thinning out the web by grinding notches on either side thereof in order to reduce the width of the chisel edge (this step being also referred to as point trimming) This chisel edge operates in very bad conditions by sinking and driving back the metal, thus producing considerable overheating, a high thrust, a rapid wear as well as radial deflection of the drill at the expense of precision. The least radial asymmetry introduced into the sharpening operation increases these deflections. Under these conditions, preliminary holes are frequently required.

It is the object of the present invention to provide a method of sharpening twist drills of the type comprising at least two symmetric lips each provided with a cutting edge, whereby the abovementioned inconveniences are reduced considerably by eliminating the conventional point edge and simplifying considerably the sharpening operation in comparison with conventional and known methods.

This sharpening method is characterized in that the twist drill point is ground to impart a pyramidal configuration thereto, this pyramid-like point being centered automatically to the twist drill axis.

A first grinding plane provides a ground surface giving the rake angle of the cutting lip; a second grinding plane provides another relief surface behind the rake surface, and a third grinding plane cuts radially towards the outer diameter a limited portion of the web. The facet formed by said first and third planes in all the twist drill lips constitute the above-mentioned point pyramid wherein the edges forming the major angle are the negative cutting edges in the web region.

The acute-angle edges of the pyramid operate as actual negative cutting elements, thus eliminating any detrimental metal driving effect. The twist drill web can be reinforced without any inconvenience as far as the metal cutting action is concerned, thus affording a faster and more accurate drilling for a lesser power consumption, together with a reduced wear.

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Other features characterizing this invention will appear as the following description proceeds with reference to the accompanying drawing illustrating diagrammatically by way of example the various steps of the twist drill sharpening method of this invention. In the drawing:

FIG. 1 is an end view of the twist drill point sharpened according to the method of this invention;

FIG. 2 is an elevational view of the tip of the twist drill shown in FIG. 1;

FIG. 3 is a perspective view showing a device for sharpening twist drills according to the method of this invention, this device comprising one grinding wheel and one twist-drill positioning support, and

FIGS. 4 and 5 show diagrammatically, respectively in elevation view and in lateral view, a three-grinding wheel sharpening device, these two views being however independent.

Referring first to FIGS. 1 and 2 it will be seen that to obtain a proper point 1 of a twist drill 2 for example of the type comprising two lips 3 and 3 providing the cutting edges, the sharpening or grinding operation is carried out in three grinding planes or surfaces for each cutting edge of the point, the same planes being obtained for the opposite or symmetric cutting edge by turning the twist drill through about its axis.

A first grinding plane provides the rake of lip 3 by forming a facet 4. A second grinding plane provides a lip relief facet 5 behind the rake facet 4. A third grinding plane provides a radial limitation, towards the outer diameter, of the twist-drill web region by cutting this region to form a facet 6. The planes of both facets 5 and 6 intersect the plane of facet 4 along a common straight line 7 lying in a plane containing the twist-drill axis A-A and constituting the point cutting edge.

By rotating the twist-drill through 180 as mentioned hereinabove the three symmetric surfaces 4 5 and 6 are obtained by grinding together with the line 7 lying in the same axial plane as line 7.

The facets 4, 6 and 4 6 of the two symmetric lips 3 and 3 constitute the faces of the pyramid.

The mutual intersection of the facets 4 and 6 on the one hand, and 6 and 4 on the other hand, of said lips, provides the point or chisel edges 8 and 8 lying in the same axial plane. The edges 7, 7 8 and 8 form at their intersection the vertex of the pyramid constituting the self-centering point of the twist-drill, which is located exactly on the axis of the twist-drill.

The above-described three surfaces are ground by using a straight-type cup grinding wheel. The rakes are constant along the cutting edges in a plane perpendicular to these edges. The edges forming the major angle are the negative cutting edges in the web portion of the twistdrill.

The sharpening operation is carried out by generation on the working face of the straight-type cup-shaped grinding wheel, thus eliminating any diamond-shaping or dressing of this face for performing this operation. The sharpening operation according to the method of this invention can be carried out on conventional twist-drill sharpening machines, as will be described hereinafter with reference to specific examples.

In a first example, the twist-drill sharpening device illustrated diagrammatically in FIG. 3 comprises a single cup-shaped grinding wheel 9 rotatably driven about the axis of its shank 10 but held in a fixed position.

The vertical plane of the grinding face 11 of this Wheel comprises the horizontal axis B-B about which the E- shaped support 12 of the twist-drill carrier 13 is pivotally mounted; this axis BB is coincident with the straight lines 7, 7 converging to the vertex of the twist drill 2.

The bed 14 supporting the support 12 is movable horizontally as shown by the arrows f and 1.

The twist-drill support 12 can be set to pivot through different angular amplitudes about the axis BB for grinding the sharpening surfaces 4, 5 and 6 described hereinabove.

The twist-drill carrier 13 proper is adapted to pivot about a pivot pin 15 carried by the support 12 for accurately adjusting the point angle.

An adjustable stop (not shown in the drawing) is also provided for limiting the movement of translation of the bed 14 and therefore the width of the face 6 cut in the web region.

The axis A-A of twist-drill 2 and the axis CC about which the twist-drill carrier is pivoted converge to a point I on axis B--B about which the E-shaped support 12 is pivotally mounted.

A stop 16 lying in the vertical grinding plane is scored with parallel horizontal lines and angularly adjustable to permit of indexing the twist-drill in a preselected position before commencing the sharpening operation in order to restore the cutting edge in a horizontal plane upon completion of the sharpening or grinding operation.

A diamond point 17 is provided for dressing the grinding wheel 9 after taking up the wear.

The device and method described hereinabove are applicable to all sharpening machines providing two perpendicular motions, i.e. one for the feed movement along the grinding wheel surface and the other for adjusting the grinding wheel feed movement.

When large series of twist-drills are to be sharpened a three-grinding wheel sharpener of the type illustrated diagrammatically in FIGS. 4 and 5 may advantageously be used for carrying out the method of this invention, as this arrangement greatly simplifies the twist-drill mountmg.

In this three-grinding wheel sharpener the wheels 18, 19 and are rotatably mounted on a common stationary semi-cylindrical cradle 21 on which each grinding wheel can be set angularly according to the values of the threegrinding planes to be obtained. Thus, for instance, grinding wheel 18 will grind the facet 4, grinding wheels 19 and 20 (of which only the axes of rotation are shown in FIG. 5) being used for grinding the facets 5 and 6 of the twist-drill point. The axes of rotation of these grinding wheels 18, 19 and 20 intersect the axis B-B about which the supporting cradle 21 is pivotally mounted where the three planes generated by the working edges of wheels 1-8, '19 and 20 intersect each other. A diamond 17 rigid with each grinding-wheel support 22 permits the dressing or adjustment of each wheel, each grinding wheel is adjustable for translation along its axis of rotation 10.

A support 23 on which the carrier 24 of twist-drill holder 13 is movable angularly in a plane containing the axis B-B permits the adjustment of the point angle of the twist-drill. A laterally movable bed 14 provided with adjustable stops (not shown) permits the movements of translation of the twist-drill 2 past the grinding wheels 18, 19 and 20. An optical device 25 is also provided for indexing the twist-drill.

The carrier 24 of the twist-drill holder is provided with a graduated scale (not shown).

Of course, various modifications and variations may be brought to the specific forms of embodiments of the present invention which are shown and described herein, without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of sharpening twist-drills having a point, at least two lips symmetric in regard to a longitudinal axis of the twist-drill each with an end part comprising the web of the drill, a cutting edge adjacent to surfaces forming a rake, said end parts of the lips forming a point having a pyramidal configuration with a vertex centered automatically to the twist-drill longitudinal axis, grinding said configuration of said end parts of all lips in the following steps, grinding along a first plane providing a first facet forming the cutting edge of the lip and giving the rake of the lip, grinding along a second plane providing a second relief facet behind said first facet, and grinding along a third plane cutting radially toward the outer circumference of said point an area limited by said web of the twist-drill, the facets formed by said first and third grinding steps in all said twist-drill lips constituting said pyramidal point wherein the cutting edges form the pyramid edges, those of the edges thereof forming the greatest angle being negative cutting edges of the web region.

2. A method of sharpening twist-drills according to claim 1, wherein said first grinding plane intersects said second and third planes along a straight line lying in the plane containing the twist-drill longitudinal axis.

3. A method of sharpening twist-drills according to claim 1, applied to a two-lipped twist-drill, wherein the said facets formed for one lip by said grinding steps are obtained automatically for the other lip by rotating the twist-drill through about its longitudinal axis for grinding symmetric faces in relation to said longitudinal axis.

4. A method of sharpening twist-drills according to claim 2, wherein the twist-drill to be sharpened is movable bodily in translation parallel to a horizontal axis coinciding with said straight line on which said three grinding planes grinding said three facets intersect, said grinding planes being performed by three separate grinding means each adjustable to a proper angular position about said horizontal axis, the complete sharpening of a radial cutting edge of said twist-drill point being performed by a single adjustment of the angular position and by a singular movement of translation of said twist-drill limited by a stop for the grinding of said third facet in the web region.

References Cited UNITED STATES PATENTS 2,328,549 9/1943 Eich et al. 5l288 X 2,369,642 2/1945 Benning 51-219 2,404,048 7/1946 Gepfert 77-70 2,932,135 4/1960 Tatar 51-219 X LESTER M. SW-lNGLE, Primary Examiner US. Cl. X.R. 5l219 R 

